Various methods for manufacturing solid and semisolid polymers from hydrocarbons, for example, from 1-olefins have been developed. In one such method olefins, such as, ethylene, propylene, or butene are polymerized in the presence of catalysts in hydrocarbon diluents or with monomers themselves acting as diluents. The reactants are then kept in the liquid phase by maintaining a proper pressure in the polymerization reactor. When the polymer is insoluble or only slightly soluble in the diluent, the polymer product forms as particles and therefore the product flow consists of a suspension formed by polymer particles, diluents and monomers. This product flow is usually transferred to a polymer separation tank, where solids and liquid and gaseous constituents are separated from each other.
One reactor type applied in such methods is a continuous pipe reactor forming a loop, where the polymerization is carried out in a turbulent flow circulating in the loop. The product containing polymer, diluents and monomers is taken from the loop reactor either continuously or more usually periodically through a discharge valve and introduced into a separator, where the polymer is separated by lowering the pressure.
A problem frequently encountered especially in loop reactors is the adhering of the polymer particles to reactor walls. Even small polymer amounts cause that the smoothness of the inner face of the reactor disappears, whereafter the adhering accelerates and, in the worst case, causes the blocking of the reactor. A polymer layer on the inner face of the reactor increases essentially the flow resistance of the polymer suspension and the pumping power required. At the same time the heat transfer efficiency of the reactor decreases and makes the temperature control more difficult. If high polymerization temperatures are used, it may result in the melting of the polymer.
Further, the quality of the product is substantially impaired by polymer agglomerations which have stuck to the inner wall of a reactor and which come off it at some stage. The polymer material which has adhered and which comes off later has a different residence time and, hence, a different molecular weight from those of a material that has not stuck, whereupon a desired molecular structure is not achieved in the end product.
Attempts have been made to avoid the harmful fouling phenomenon described above by adding into diluent antistatic agents, which make the diluent more conductive and thereby prevent the formation of static electric charges at least to some extent. However, antistatic agents of that kind are usually harmful to the polymerization catalyst, because they act, at least to some extent, as catalyst poisons, thereby decreasing catalyst activity.
U.S. Pat. No. 3,956,252 proposes a nitrogen containing salt of phytic acid or a mixture of it with an alkali metal salt of an organic acid for an antistatic agent.
U.S. Pat. No. 3,995,097 proposes a mixture of an aluminum or chromium salt of an alkyl salicylic acid and an alkalimetal alkyl sulfosuccinate for an antistatic agent.
U.S. Pat. No. 4,012,574 proposes a surface-active compound, which contains one or more perfluorocarbon groups, for an antistatic agent.
U.S. Pat. No. 4,068,054 proposes a porphyrin compound either alone or together with a metal alkyl sulfosuccinate for an antistatic agent.
U.S. Pat. No. 4,182,810 proposes a mixture of a polysulphone polymer, a polymeric polyamine and an oil-soluble sulphonic acid for an antistatic agent.
The purpose of the invention is to provide a method for preventing the harmful fouling phenomenon in polymerization reactors. One object of the invention is to provide a method for preventing the harmful fouling phenomenon so that the catalyst activity does not essentially decrease. One further object of the invention is to provide a method for preventing the harmful fouling phenomenon so that the heat transfer of the polymerization reactor does not decrease essentially and so that there is provided a better residence time and molecular weight distribution of the polymer particles.